Risperidone is a new antipsychotic agent that is likely to be available in the USA for general use in the near future. It has demonstrated superior efficacy to haloperidol for positive and negative symptoms and is associated with low levels of extrapyramidal symptoms. Clozapine is the only other antipsychotic drug that has demonstrated superior efficacy compared to conventional neuroleptics, and it too is associated with low levels of extraphramidal symptoms. Preclinical studies indicate risperidone has a unique biochemical profile in that it is more highly potent at the dopamine D2 and serotonin 5HT2 receptors than clozapine. The purpose of this study is to compare risperidone's neurochemical properties with those of the atypical neuroleptic clozapine. In addition, the relationship between risperidone's biochemical effects and clinical efficacy will be examined. The biochemical variables are D2 occupancy as determined by IBZM/SPECT and CSF and plasma metabolite levels.